Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Pat. Nos. 6,016,038 and 6,211,626, incorporated herein by reference.
Some implementations of LEDs utilize a DC power supply to drive the LEDs. For example, shelf lighting and lighting for refrigerators in super markets and other stores may include LED-based light sources that utilize a DC power supply. LEDs in such implementations may be dimmable via a dimmer that is interposed between the DC power supply and the LEDs and that controls the power delivered to the LEDs through pulse width modulation (PWM). A current source may be paired with the LEDs to provide the required current for the LEDs. Although such implementations provide for dimming of LEDs, they do not provide for change of the color of the light output generated by the LEDs.
Thus, there is a need in the art to provide a LED lighting unit that may be operated by a DC power supply and that provides dimming control and color control.